This invention relates to a constant printing pressure mechanism for a hand operated labeler for clearly and precisely printing the labels on a label strip irrespective of the strength and speed of the squeezing and releasing of the hand lever or the trigger of the labeler. Further, the constant pressure mechanism of the present invention is used in a hand labeler of the type which imprints ordinary numerals or marks or OCR (optical character recognition) letters or bar codes on the labels of a label strip. The label strip is comprised of a carrier strip coated with a releasing agent on its surface and a chain of same sized labels coated with pressure-sensitive adhesive on their rear surfaces and affixed on the surface of the carrier strip. Squeezing and releasing of the hand lever not only imprints labels, it also peels the printed labels from the carrier strip so that they may be applied on the surfaces of desired articles.
In the operation of the conventional hand labelers, the printing pressure of the type face against the label surface varies according to the manual force applied upon squeezing of the hand lever and upon the speed of a squeeze. The quantity of ink applied to the label surface by the type face varies in each imprinting operation, depending on the printing pressure and the duration of one squeezing of the hand lever. Therefore, labels could not be consistently printed with clear and balanced letters by using the conventional hand labelers.
For example, in the hand labeler disclosed in U.S. Pat. No. 3,265,553, a hand lever is pivotally attached to the hand grip that is integrally formed on the rear portion of the machine frame, while the front portion of the hand lever is integrally provided with a yoke carrying a printing device. The printing device is vertically moved toward the label together with the yoke as the hand lever is squeezed. Depending upon how strongly the hand lever is squeezed each printing stroke, the printing pressure of the type face against the label surface correspondingly varies. Furthermore, when the duration of each squeezing operation is different, the quantity of ink applied to the label surface varies, even when the printing pressure is constant. Therefore, clear, precise, predictable printing on labels cannot be expected.
Furthermore, in the hand labeler disclosed in Federal Republic of Germany Offenlegungsschrift DT-OS No. 1,909,900, a printing device is affixed to the machine frame and a press platen to press labels against the types of a printing device is attached to the front portion of rocking levers formed separately from the hand lever. When the hand lever is squeezed, the press platen is raised and the label on the platen is forced against the types. When the hand lever is released, the press platen is lowered. Therefore, like the above-mentioned hand labeler of U.S. Pat. No. 3,265,553, because the hand lever is squeezed with varying force, the printing pressure of the printing device against the label changes during each imprinting. In addition, the quantity of ink transferred varies with the duration of a squeeze of the hand lever, even when the printing pressure is not changed. Therefore, clear and precise label printing cannot also be expected by this hand labeler.
In the hand labeler disclosed in U.S. Pat. No. 3,420,172, the hand lever pivots relative to the grip which is integral with the machine frame. An inking roller is attached to the upper extension of the hand lever. The supporting arm of the printing head is pivotally attached to the upper portion of the machine frame. The printing head is pressed toward the labels on the platen by the tension of a spring. When the hand lever is squeezed, a cam formed on the upper end of the hand lever contacts the follower of the inking roller supporting arm, and ink is applied to the type face of the printing head by the inking roller. At the same time, the printing head is pivoted up. When the hand lever is thereafter released, the printing head is forced down by the spring and the label is thus printed. According to this structure, the label is printed with the same printing pressure, independent of the squeezing force applied to the hand lever. However, the printing head is kept in contact with the label a vaying length of time, so that the quantity of ink transferred to the label differs according to the time period of such contact. Therefore, clear printing on the labels is not always expected with this apparatus. Further, in the hand labeler of this type, because the printing head moves downward as it prints, precise printing cannot be attained owing to the vibration of the printing head caused by its own weight and its motion.
Precise and clear imprinting of labels has never been attainable with the conventional hand labelers. However, such labelers could be used for ordinary purposes of printing only the visually recognizable numerals and letters on labels attached to merchandise in stores, and the like purposes. In these situations, even when the imprinted characters are somewhat unclear, imprecise, overinked, underinked or uneven, customers or cashiers can still read them without problem.
Recently, however, the employment of what is called POS (point of sales) control systems is gradually increasing, particularly in large stores. In a POS control system, OCR letters or bar codes indicating the maker, the item, colors, sizes, seasons, grades, materials, prices and the like are printed on labels. The printed labels are then applied to commodities such as clothing and foods. When the commodities are sold, the data printed on the attached labels are read and treated by an optical reader.
It is necessary that the OCR letters or bar codes be printed clearly and precisely in order that they be capable of being read by optical means. However, as disclosed in the foregoing, the conventional hand labelers are not suitable for printing such OCR letters and bar codes since the ink density and clarity of printing are different in each operation and the precision of printing is unsatisfactory.